CHEMICAL AND PHYSIOLOGICAL STUDIES. 



163 



formed at first in plastids,* and by the time the tuber is full 

 grown, all the plastids have been converted into starch. During 

 the examination of the chloroplasts in the cells of ValJisneria 



Fig. Ill Various Starch-geains from Cells of the Potato-tuber. 



1. Small granules in which the first signs of a hilum and concentric 

 laminae can be detected. 2, 3, 4. Grains of various shapes and sizes 

 in which the hilum and lamination are well marked. 5, 6. Grains in 

 which the starch is deposited regularly at first, and subsequently 

 somewhat irregularly. 7. A plastid from the rhizome of Ins 

 germanica, showing the formation of starch at both ends. 8. The 

 resulting dumb-bell shaped granules formed from 7. 9. Effect of 

 boiling water upon a starch-grain : the outer envelope is the farinose, 

 the inner granular portion (stained with iodine) is the granulose. 



* Some of the starch is, however, formed in the tuber by the trans- 

 location of carbohydrate from the cells of remote parts, and starch is 

 then reformed by the plastids from sugar, &c. 



